In the treatment of diseases of the cardiovascular system, a variety of treatment devices are delivered by a catheter to a desired location in a bodily vessel. These treatment devices include balloons, stents and optical fibers carrying laser light.
In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. An over the wire (OTW) balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The OTW catheter may have a guide wire lumen which is as long as the catheter or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter. Alternatively, a fixed wire balloon may be used. This device features a guide wire which is affixed to the catheter and cannot be removed.
To help prevent arterial closure, repair dissection, or prevent restenosis, a physician can implant an intravascular prosthesis, or a stent, for maintaining vascular patency inside the artery at the lesion. The stent may either be a self-expanding stent or a balloon expandable stent. For the latter type, the stent is often delivered on a balloon and the balloon is used to expand the stent. The self-expanding stents may be made of shape memory materials such as nitinol or constructed of regular metals but of a design which exhibits self expansion characteristics.
Catheters are also used to deliver optical fibers carrying laser light to provide controlled delivery of a laser beam for treatment of atherosclerotic disease.
It is often desirable to provide a retractable sheath as a cover over a treatment device until the treatment device is positioned. At that point, the retractable sheath is removed and the treatment device delivered to the desired location.
Consequently, as the retractable sheath of a catheter is retracted to allow for deployment of a stent or other treatment device, the tip of the catheter has a tendency to move. In particular, where the catheter traverses a twisted, curved pathway, a portion of the catheter, including the tip, upon retraction of the sheath, will have a tendency to move either to the inside of the curve or to the outside of the curve from its position in the center of the pathway resulting in the tip moving forward. This movement of the tip can complicate the precise deployment of a stent or other treatment device as the practitioner cannot be certain of the exact location of the catheter tip as the treatment device is deployed.
In an effort to address this difficulty, the present invention is directed toward a catheter in which the movement of the tip associated with retraction of the catheter is eliminated via a locking means. Two principal approaches are used to accomplish this goal. In one approach, the guidewire is locked to the tip prior to retraction of the sheath. In the other approach, the catheter shaft exhibits a controllable variable flexibility. Motion of the tip is prevented by increasing the rigidity of the catheter prior to retraction of the sheath.